Early environments that developing organisms encounter during ontogeny have profound and persistent effects throughout life. In human offspring, variation in early family environments and gestational endocrine environments can profoundly shape multiple biosocial parameters, including sociality and behavior, stress reactivity, pubertal timing, and later parental style. We will examine the impact of early environments on development in a marmoset model that is relevant to human development. Marmoset development occurs in a family system, with multiple caregivers providing qualitatively and quantitatively different forms of care. Further, mothers often conceive immediately postpartum, leading to elevated maternal steroid hormones (including androgens) that can impact both developing fetuses (via placental transfer) and nursing offspring (via milk-borne steroids), a condition often found in human females (e.g., polycystic ovarian syndrome). In addition, female marmosets also exhibit elevated and varying levels of glucocorticoid hormones during pregnancy, suggesting that offspring may be differentially affected. The studies described in this application will address 3 aims: 1) Does variation in early care produce phenotypic variation in behavioral, physiological, and parental care?; 2) How is behavioral, somatic, and reproductive development shaped by pre- and postnatal exogenous steroids in marmosets?; and 3) does variation in gestational exposure to glucocorticoid hormone alter developmental trajectories, particularly in the stress system and somatic development? Using an established colony of marmosets, we will evaluate the links between early care received by marmosets and later parental care toward their own offspring. Secondly, we will look for associations among maternal androgens during gestation and during lactation (including concentrations in milk) and subsequent biobehavioral parameters. Finally, we will monitor cortisol responses to a standardized psychosocial stressor to evaluate whether exposure to high fetal glucocorticoids programs marmosets to be stress-responsive.